1. Field of the Invention
The present invention relates to pre-insulated piping systems, and more specifically to a method for installing such systems which avoids preexisting obstacles in the pathway of the pipeline while eliminating the need for valve pits or more complicated placement techniques.
2. Description of the Prior Art
There are many instances in which insulated pipelines are needed. For example, distributed HVAC (heating, ventilation and air conditioning) applications utilize chilled water for cooling and steam for heating. The chiller and boiler are typically contained in a central location and the chilled water and steam are distributed to other locations. For example, on a school or college campus, the chiller and boiler may be located in a power plant building. The chilled water and steam are distributed to classrooms in separate buildings.
A set of insulated pipelines is used to convey the chilled water from the chiller to other locations and back to the chiller. Another set of insulated pipelines is used to carry the steam from the boiler to the other locations and back to the boiler. The insulated pipelines are usually located underground.
Pre-insulated pipe is conventional and commercially available. There are predominately two types of such piping systems in use: Class-A drainable dryable testable (DDT); and polyurethane or polyisocyanurate “bonded” foam systems. Both of these systems use an inner carrier pipe to convey fluid. Although steel is commonly used for the inner pipe which carries the media to be piped, copper or aluminum or other metals as well as fiberglass, PVC, and similar materials may be utilized, as well. Around the outside of the steel pipe is a layer of insulating foam such as, for example, polyisocyanurate foam. Around the outside of the foam is a jacket of hard thermoplastic (such as high density polyethylene, HDPE). The foam has set up or cured within the outer jacket so as to bond to the jacket and to the inner pipe. The plastic jacket protects the foam from mechanical damage and also provides a water tight seal to prevent corrosion of the steel pipe. In the bonded type system, the foam and outer jacket do not move relative to the inner pipe. In the Class-A type system, on the other hand, the insulated inner pipe is designed to move independently of the associated outer jacket. In fact, there is an air gap between the inner pipe and outer carrier pipe in the class-A type system.
The bonded foam piping systems are normally installed in a subterranean location by digging a trench from the surface and by then laying down the pipe. Thus, in pre-insulated piping systems of the type under consideration, one of the principal expenses in the overall cost of the job is the cost of trenching. As the depth of the trench increases, the water table depth is approached in some locations. This can lead to additional problems with de-watering the trench, and the like. The deeper the trench being dug, the greater the need for shoring up the excavation to meet applicable safety standards for workers. Obviously, the nearer the pipeline can be laid to the surface the better, at least as far as lessening the excavation costs and avoiding some of the previously mentioned problems.
However, in any given pipeline installation project, the path of the pipeline tends to be obstructed, at points, by various types of of above ground or underground structures. For example, the path of the pipeline may encounter a buried “duct bank” containing electrical wires or cables, fiber optic cables, and the like. The wires/cables are typically buried in concrete, with the resulting duct bank being a foot or more in cross sectional area.
In the past, it was generally necessary to either take the pipeline deeper to go below the duct bank, or to build in place a “valve pit” or manhole to allow a change in elevation of the pipeline. This added greatly to the cost of the installation. In addition, with steam lines, it was necessary to provide the appropriate “slope” to the pipe line, along with the change in elevation, and to provide appropriate condensate collection and drain points to prevent the buildup of condensate in the overall pipeline.
Despite the advances which have been made in pre-insulated piping systems in recent years, and in the installation techniques which are used to place the pipelines in the desired subterranean locations, a need continues to exist for further improvements.
For example, a need exists to provide an installation technique which allows a pre-insulated pipeline to be routed so as to avoid existing obstacles in the path of the pipeline, without greatly increasing the depth of the overall pipeline.
A need also exists for such an installation technique which eliminates the need for adding valve pits or manholes in order to accommodate changes in elevation in the pipeline.
A need also exists for such an installation method which utilizes many of the conventionally available materials and installation techniques commonly used in the industry and which is relatively simple in design and economical to implement.